Regular Expressions 101

Pro

^start of line

Positive Lookahead(?=\d)

\da digit

Negative Lookahead(?!0(?![.]))

0the literal 0 (48₁₀ / 60₈ / 30₁₆)

Negative Lookahead(?![.])

Character Class[.]

.the literal . (46₁₀ / 56₈ / 2E₁₆)

Non-Capturing Group(?:\d{0,3})

\d{0,3}a digit, repeated between 0 and 3 times

Non-Capturing Group(?:[.]\d{1,3})?

?repeats the group contents below at most once:

Character Class[.]

.the literal . (46₁₀ / 56₈ / 2E₁₆)

\d{1,3}a digit, repeated between 1 and 3 times

$end of line

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

Detailed match information will be displayed here automatically.

25 tokens

^(?=\d)(?!0(?![.]))(?:\d{0,3})(?:[.]\d{1,3})?$